chore: bump anthropic-sdk-go to include DirectEncoder optimization (#24)

Updates coder/anthropic-sdk-go to a31d7d0e7067 which adds the
DirectEncoder interface, cutting marshal allocation overhead by ~66%
for nested SDK types.

See: coder/anthropic-sdk-go#7

Author: johnstcn

go.mod

@@ -89,4 +89,4 @@ replace github.com/openai/openai-go/v3 => github.com/kylecarbs/openai-go/v3 v3.0
 
 // coder/coder uses a fork of charmbracelet's fork of the Anthropic Go SDK with some
 // additional performance improvements. This is tracking the coder_2_33 branch.
-replace github.com/charmbracelet/anthropic-sdk-go => github.com/coder/anthropic-sdk-go v0.0.0-20260409105508-5711db120546
+replace github.com/charmbracelet/anthropic-sdk-go => github.com/coder/anthropic-sdk-go v0.0.0-20260415160422-a31d7d0e7067

go.sum

@@ -56,8 +56,8 @@ github.com/charmbracelet/x/json v0.2.0 h1:DqB+ZGx2h+Z+1s98HOuOyli+i97wsFQIxP2ZQA
 github.com/charmbracelet/x/json v0.2.0/go.mod h1:opFIflx2YgXgi49xVUu8gEQ21teFAxyMwvOiZhIvWNM=
 github.com/cncf/xds/go v0.0.0-20251022180443-0feb69152e9f h1:Y8xYupdHxryycyPlc9Y+bSQAYZnetRJ70VMVKm5CKI0=
 github.com/cncf/xds/go v0.0.0-20251022180443-0feb69152e9f/go.mod h1:HlzOvOjVBOfTGSRXRyY0OiCS/3J1akRGQQpRO/7zyF4=
-github.com/coder/anthropic-sdk-go v0.0.0-20260409105508-5711db120546 h1:dYAA1uo93n9r/B4Gvx76pjaeS0kBTX1lO0WX0p0uqo8=
-github.com/coder/anthropic-sdk-go v0.0.0-20260409105508-5711db120546/go.mod h1:hqlYqR7uPKOKfnNeicUbZp0Ps0GeYFlKYtwh5HGDCx8=
+github.com/coder/anthropic-sdk-go v0.0.0-20260415160422-a31d7d0e7067 h1:v1RAkUO21u0QH6UlUueSHMbgFf++BZZW41Rj6LM2eWo=
+github.com/coder/anthropic-sdk-go v0.0.0-20260415160422-a31d7d0e7067/go.mod h1:hqlYqR7uPKOKfnNeicUbZp0Ps0GeYFlKYtwh5HGDCx8=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dnaeon/go-vcr v1.2.0 h1:zHCHvJYTMh1N7xnV7zf1m1GPBF9Ad0Jk/whtQ1663qI=